STRUCTURE AND LUMINESCENCE OF THE NEUTRAL DINUCLEAR LANTHANIDE(III) COMPLEXES [(LN(API))(2)] HYDROXYPHENYL)-3-AZABUT-3-ENYL]-1,3-IMIDAZOLIDINE)

Dinuclear compounds of lanthanide(III) (Ln(3+)) ions with api(3-) [{Ln (api)}(2)] {H(3)api = 2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolin e} were synthesized and characterized in microcrystalline form and fro zen aqueous solutions in order to establish the ability of triply char ged chelates to stabilize Ln(3+)-Ln(3+) couples. The crystal structure of the [{Sm(api)}(2)] complex confirms the dinuclear sandwich binding in which the pair of Ln(3+) ions is trapped between the two chelates to yield an eight-fold ca. square antiprismatic co-ordination geometry on each Ln(3+) ion. Luminescence decay dynamic studies revealed therm al quenching of Tb3+(D-5(4)) [thermal barrier E-a approximate to (1.2 +/- 0.2) x 10(3) cm(-1)] and Eu3+(D-5(0)) [E-a approximate to (4.7 +/- 0.2) x 10(3) cm(-1)] emission from [{Tb(api)}(2)] and [{Eu(api)}(2)] respectively. Luminescence decay dynamics of homodinuclear [{Ln(api)}( 2)] (Ln = La, Gd, Eu or Tb) and heterodinuclear [{Tb1-xEux(api)}(2)] c omplexes in polycrystalline and frozen aqueous solutions as well as th e small proton NMR relaxivity of [{Gd(api)}(2)] and low toxicity (to m ice) of [{La(api)}(2)] show qualitatively that members of the [{Ln(api )}(2)] system are stable in water and merit further study in search of potentially useful tunable biomedical probes.